I. Field of the Invention
The present invention relates generally to power gain control for a power amplifier circuit and particularly to a power application circuit having greater power conservation in wireless communication device, such as a CDMA wireless phone.
2. Description of the Related Art
In many electronic environments, such as most hand-held communication systems including code-division-multiple-access (CDMA) or any form of time-division-multiple access (TDMA) technology, RF power output from a mobile unit varies in large dynamic ranges. In a CDMA radiotelephone system, multiple signals are transmitted simultaneously at the same frequency. The signals are spread with different digital codes, thus allowing detection of the desired signal while the unintended signals appear as noise or interference to the receiver. Spread spectrum systems can tolerate some interference, and the interference added by each new mobile station increases the overall interference in each cell site. Each mobile station introduces a unique level of interference, which depends on its received power level at the cell site.
The CDMA system uses power control to minimize mutual interference. A precise power control is critical to avoid excessive transmitter signal power that is responsible for contributing to the overall interference of the system. Power of the individual mobile stations varies with the distance between the mobile station and the base station and the number of other subscriber mobile stations in that base station or sector.
In a typical hand-held wireless unit, the power amplifier is biased class AB to reduce power consumption during periods of low transmit power, but power continues to be consumed. Typically an isolator is used to isolate the power amplifier from the effects of load impedance in subsequent stages. One method to avoid continuous battery draw is to employ a means to bypass the amplifier with switches, and then remove DC power from the amplifier. Such a power amplifier circuit has a power amplifier and an isolator. An RF-input is connected to a pole of a first switch. When the amplifier is on, the switch connects the RF-input to an input of the power amplifier. The RF-signal is amplified and output to the isolator, and then transmitted through the second switch to the RF-output of the power amplifier circuit. To bypass the power amplifier, the first switch connects the RF-input to the bypass path and the second switch transmits the signal to the RF-output. The switching employed introduces loss as the signal is processed. The drawback of this design is that the amplifier must overcome the added switching loss during times that higher transmit power is required. This can tend to cancel the benefits of bypassing.